Polyphase-carrier-current broadcasting system and generator



March 30-, 1926'. 1,578,881

R. D. DUNCAN, JR

POLYPHASE CARRIER CURRENT-BROADCASTING SYSTEM AND GENERATOR Filed Jan.9, 1925 2 Sheets-Sheet 1 INVENTOR 1%602'1 2 30/250 J2;

ATTORNEYS.

PW-fb m w ai/vvr WM March 30,1926. '1 5 8,88.1

R. D. DUNCAN, JR 1 POLYPHASE CARRIER CURRENT BROADCASTING SYSTEM ANDGENERATOR Filed Jan. 9, 1925 2 sneets-sfiee'r, '2 V INVENTOR PatentedMar. 30, 1926.

ROBERT :a. DUNCAN, 3a., or EAST ORANGE, NEW JERSEY, assrenon TO WIREDRADIO,

Inc, on NEW YORK, n. Y., A CORPO ATION OF DELAWARE.

IOLYPIiASE-CARRIER-CURRENT BROADCASTING SYSTEM AND GENERATOR.

Application filerl"Ja11uary 9, 1925. Serial No. 1,314.

'1 b all 10710??? i may concern: v

Be it kno'wnthat 1. ROBERT -D. DUNCAN,

J12, a citizen ofthe United States, residing at East- Orangc, in thecounty of Essex,- State of New Jersey-have invented certain new anduseful Improvements in Polyphase- Carrier-Current Broadcasting Systemsand Generators; andl do hereby. declare the following to be a full,clear, and exact description of the invention, such as will enableothers skilled in the art to which appertains to make and use the same.

In high frequency carrier-current broadcasting systems superimposed onelectric" carrier over a poly-phase system, but practical experlence hasunheated that thls'can-' not be done consistentlyenough for com-fmercial broadcasting on a large scale.

Almost from the very beginning of the extensive research work which hasbeen carried on in the wired radio broadcasting field it'has beenrealized that more even and "satisfactory carrier current distributioncould be effected on poly-phase power lines byithe' use of poly-phasecarriers, but in so far as,

it has been possible to ascertain, there has heretofore been noknowngenerator of poly-phase high frequency oscillations of The presentinvention practical character. is directed in part to such a generatorand, in part, to a W1redrad1o broadcasting system of the poly-phase typeinch-more specifically;

to a system wherein single phase high fre quency oscillations areconverted nto poly-,

phase high frequency oscillations and superimposed upon the lowfrequency'p'ower currents on a poly phase power t *ansmission line. I

The poly-phase system in part, upon the method of producing phasedisplacement disclosed on pages 352 and of a publication entitledlVireless Telegraphy, by Dr. J. Zenueck, McGraw-Hill Book Company, Inc,15))15, under! the caption, Production of any desired phase differenceswith undamped oscillations, wherein it is shown that between twoloosely-coupled resdrawings, in; which i Fig-L531 is a schematic circuitdiagrainfillus tinting-the underlying principles whereby "singlephase'oscillations are converted into ,tially complete and generatorherein dealt with are devolopments based,

onant circuits, the currents are 99 out of phase and that'a circularrotating magnetic field may be produced bytwo coils having equalmagnetic fields with coincident magnetic centers and axes atright-angles and wherein the currents are out of phase.

In accordance with the preferred embodiment of this invention singlephase high frequency oscillations. are produced by means of a mastervacuum tube oscillator;

"and high frequency currents of, the master oscillator frequ'encyybutwith a phase difference of. 90- are produced by loosely coupling tworesonant circuits, one of whichis supfplied witlr high frequency currentby the master oscillatoli ith the circular magnetic field thus producedin the manner hereiubeforereterred to from the single phaseoscillationsgenerated by the master oscillator, a carrier current of anynumber of phases may be produced by arranging a corresponding number ofcoilsin the rotating magnetic lieldswith their axes at the properangular relation toeach other, :In practise gthc three-phase or otherpoly-phase carrier thus. produced 'isamplified, modulated and impressedupon the power transmission lines at the central power stationorsub-station as may be convenient, and-thus .over thepower network.

distributed The inveutio will be more clearly under-- stood;'from thefollowing detailed description, in conyunction' with theaccompanyingpoly phase oscillations. p

Figs. .2 and are schematic circuit diagrams serving to illustratealternative connections of the'coilsin which the poly-phase currentsare, generated tothepower transmission lines, and r Fig. ris a circuitdiagram of a substanthree-phase wired radio transm tter. v r

;In the schematic diagram of Fig. 1'l is'a. single phase high.frequencyoscillator of anyft-ype and ,niay conveniently be a vacuumtube oscillator This is referred to as the anaster oscillator and. iscoupled.

througlra transformer 2, to a tunable circuit including thesecondary=-w1nd1ng 6, an inductance 5,;coil e t aiid variable condenser3. The tunable circuit 3, 4, 5, 6 is loosely coupled to a secondarycircuit comprising the variable condenser 7, coil 8 and inductance 9thecoupling between the circuits being effected through the variablycoupledinductances 5 and 9.

It is found that when the circuits 3, 4, 5, G and 7 8, 9 respectivelyare quite loosely coupled and. the latter tuned exactly or approximatelyto the frequency ofthe master oscillator, the currents in these twocircuits are approximately or exactly 90 out of phase.

In some cases it is found that circuit 7-, 8, 9 must be tuned quiteexactly to the master frequency while in other cases better results areobtained when this circuit is more or less detuned with respect to. themaster frequency. Circuit 3, 4, 5, 6 is not necessarily tuned to themaster frequency but maybe so. Coils 4 and 8 are so disposed withrelation to each other that their axes are at right angles and their"centers of magnetic. flux are coincident. The center of magnetic fluxis indicated on Fig. 1 asa point in each coil which is centrally locatedwith respect to the circumference and the longitudinal extremities. Itmay be demonstrated that if the currents in the coils 4 and 8 are 90 outofphase with each other and the magnetic fields of the coils are equal,the combined magnetic field will rotate about the coincident centers ofmagnetic flux and the result will be the same as inthe case of a singlecoil rotating about its .own center of magnetic flux. In other words theresultant magnetic field is the same as in a dynamo-electric machinehaving a rotating field.

Three co'ls 10, 11, 12 are shown having their planes intersecting atangles of 60 and their centers of magnetic flux coincident with that ofthe coils 4 and 8. These coils being wound in the proper direction andbeing disposed in the rotating magnetic field will have generated inthem currents which are .120 apart and if the terminals of each coil areconnected together in star or delta:

as indicated in the circuits of Figs. ,2 and 3 and also'connected to aload circuit such as a three-phase power transmission line comprisingconductors 16, 1 and 18, three-phase high frequency currents aregenerated in these coils and impressed upon the three phase powertransmission lines. Condensers 13, 14, 15 are inserted in the powerlines for the purpose of preventing the low frequency power currentsbeing short circuited through the coils 10, 11, 12 and furthermore,function to tune the power lines; 'The transmitter diagrammaticallyillustrated in Fig. 4 comprises a master oscillator 1, phase displacingcircuits 19 and 20, a high frequency amplifier 21 and a modulator 22.The master oscillator 1 is one of the wellknown vacuum'tube oscillatorcircuits and needs no description. This master oscillator I isinductively coupled through windings 2 and 6, corresponding to thosebearing the same reference numerals in Fig. 1, to the tunable phasedisplacing circuit 19, comprising elements 3, 4, 5, 6, corresponding tothe circuit 3, 4, 5, 6 of Fig. 1, and in addition, varionieter 23 andammeters 24 and 25 are included in this circuit. The secondary phasedisplacing circuit corresponding with secondary circuit 7, 8, 9, of Fig.1, includes in addition to elements 7', 8, 9, a variometer 26 and anammeter 27. The ammeter 25 is common to both circuits l9 and 20. Coils421ml 3 of Fig. 4 are arranged with respect to each other in thesame'way as coils 4 and rug- Coils 10, 11, 12 of Fig. 4 correspond withthe coils having the same reference numerals in Fig. 1. These coilsshould be physic'ally'disposed with respect to coils 4 and 8 in the samemanner as described in connection with Fig. 1,- that is to say theyshould be so arranged that three-,phase currents will be generated inthem by the rotat-' 'ing magnetic field about .coils 4 and 8. Coils 10,11, 12 are shown connected in star and are inc'luded in the inputcircuit of three-parallel vacuum 'tube amplifiers 28,

29, 30. It will be noted that the common I terminal of these three coilsis connected to the grounded filaments while the remaining terminals areconnected to the grids of tubes 28, 29 and 30 respectively. Theplate-film ment' or output circuits of amplifier tubes 28, 29, 30include inductances 31, 32, 33,

respectively, each in series with a condenser, .34, 35, 36. Theseinductances are coupled threeparallel amplifier tubes 43, 44 and 45.

The parallel input circuits of these tubes includes thesecondarywinding-of a trans-- former 46 in the primary circuitof which is amicrophone 47 and a battery 48. A grid biasing battery 49 may also beinserted in the input circuit of the modulator tubes.-

A generator 50 supplies direct current to the plate circuits of all theVacuum tubes. A high inductance coil 51 functions in the well knownmanner to effect plate potential variations at the'ampli'fier tubes inaccordance with the audio frequency variations impressed 'on microphone47. Three-radio frequency choke coils 53 are inserted-respectively inthe plate-current supply circuits of the amplifier tubes 28, 39, 30.These coils serveto prevent the shunting of high frefrequencythree-phase power supply and quency currents from the output side of theamplifier through the modulator tube.

In operation varior'neters 23 and 26 in circuits 19 and 20 respectively,and condenser 7 are ordinarily adjusted until the ammcters 24 and 27show the same reading. If, under these conditions and with the properdegree of coupling between inductances 5 and 9 the reading of ammetershould be equal to times the reading of either of the other ammeters.

In the particular system of Fig. 4 modulation is effected at theamplifier tubes, rather than at the oscillator tube. Modulation iseffected in this case through diversion of current from the platecircuit of the amplifier tube through the parallel plate circuit of themodulator tubes. It is to be understood that the three-phasetransmission line 16, 17, 18 is connected to a source of low that itextends to local distributing points where the phases are branchedofi.usually through stepdown transformersto the various power andlighting subscribers and that these subscribers or some of them areprovided with receiving sets which are connected through lamp sockets orotherwise to .these respective branches. It will furthermore beunderstood that each. branch line, except in special cases, conductsonly one of the three-phases of each frequency, that is,

the power frequency and carrier frequency.

It is apparent that the invention herein disclosed is applicable for theproduction of poly-phase high frequency carrier currents having anynumber of phases, at least within the limit of the number of phasesemployed in power transmission systems.

I claim: I

1. A broadcasting system comprising a poly-phase electric. powertransmission line, a source of poly-phase high frequency carrier currentconnected to said power transmissiomline, means for modulating saidcarrier current in accordance with signals to be transmltted over saidpower transmission line, and receiving apparatus responsive to themodulated carrier current and operative to reproduce said signals, saidreceiving appar'atus being connected to said power transmission line.

2. A broadcasting system comprising a poly-phase electric powertransmission line, a source of poly-phase hi h frequency carriercurrent, the phases-o said carrier current being the same in number asthose of said line, said source of carrier current being so connected tosaid line that each power phase has superimposed upon it one of thephases of said p0 y-phase high carrier current, means for mo ulatingsaid carrier current in accordance with signals to lbe transmitted, anda plurality of receivfrequency ing stations each of which is connectedto one phase only of said transmission line, there being one or more ofsaid receiving stations connected to each phase of said transmissionline, said receiving stations each comprising apparatus responsive tomodulated carrier currents to reproduce signals transmitted thereby oversaid transmission line. r 1

3. The combination with an electric power distribution system comprisinga poly-phase power transmission line, of a poly-phase carrier currentgenerator connected to said line, a plurality of receiving stationsconnected to said line, each of said receiving stations comprising meansresponsive to modulated hi h frequency carrier currents received fromsaid line to reproduce sound waves corresponding to the modulations ofsaid carrier currents, said generator comprising a singlephase masteroscillator in combination with phase displacing circuit connectionswhereby high frequency currents having a phase difference ofapproximately are produced,

' circuit means utilizing said last mentioned power transmission line,of av three-phase high frequency carrier current generator comprising asource of single phase hi h frequency oscillations, a pair of tunableoosely coupled circuits at least one of which is tuned to the frequencyof said single-phase oscillations and one of which is supplied withsingle-phase oscillations from said source, each of said tunablecircuits including a coil, the centers of magneticflux of which arecoincident and the axes of which are at right angles, the magneticfields of said coils being substantially equal, three secondary coilshaving their axes angularly displaced by approximately 60, saidsecondary coils being situated in said magnetic field, the arrangementbeing such that threephase high frequency carrier currents are inducedin said. secondary coils, means'for amplifying and impressing saidthree-phase transmitted.

In testimony whereof I atfix my signature.

ROBERT D. DUNCAN, J R.

' carrier currents on said power transmission line, and means formodulating said carrler currents in accordance With signals to be

